The present, invention relates generally to semiconductor devices, and in particular to drivers for word lines in memory devices.
Memory devices often reside in computers and electronic products to store data. A memory device has many memory cells, each holding an electrical charge that represents a bit of data. External data is stored in the memory cells during a write operation. The stored data is retrieved from the memory cells during a read operation. The write and read operations are memory access operations.
A typical memory device has a number of control lines, each connecting to one or more corresponding memory cells. During a memory access operation, the memory device controls a voltage on each control line to access the memory cells to either store data or retrieve data. Control lines of these types are usually called word lines.
A typical memory device has a number of word line drivers. Each word line driver drives a corresponding word line to various voltages. For example, some memory devices have word line drivers that drive the corresponding word lines to a positive voltage during a memory access operation. After the memory access operation, the word line drivers drive the corresponding word lines to a negative voltage.
Some memory devices have word line drivers that drive the corresponding word lines from a positive voltage to a negative voltage using one discharge path. In some of these memory devices, driving the word lines from a positive voltage to a negative voltage using one discharge path generates excessive noise, causing the memory device to perform inefficiently.
The present invention provides circuits and methods for driving word lines of memory devices to a negative voltage without generating excessive noise.
In one aspect, a memory device includes a memory cell connected to a word line. A word line driver drives the word line to various voltages. The word line driver has multiple paths: a first path and a second path, each connecting to the word line. The first path serves as both a charging path and a discharging path. The second path serves as another discharging path. During a first state of a control signal, the first path charges the word line to a positive voltage. During a second state of the control signal, the first path discharges the word line to ground. The second path further discharges the word line from ground to a negative voltage during the second state of the control signal.
Another aspect offers a method that includes driving a word line connected to a memory cell to a first voltage via a first path to access the memory cell. After the memory is accessed, the method drives the word line to a second voltage via the first path. The method further drives the word line from the second voltage to a third voltage via a second path. The first voltage, the second voltage, and the third voltage are unequal.